title: Right fusiform response patterns reflect visual object identity rather than semantic similarity.
abstract: We previously reported the neuropsychological consequences of a lesion confined to the middle and posterior part of the right fusiform gyrus (case JA) causing a partial loss of knowledge of visual attributes of concrete entities in the absence of category-selectivity (animate versus inanimate). We interpreted this in the context of a two-step model that distinguishes structural description knowledge from associative-semantic processing and implicated the lesioned area in the former process. To test this hypothesis in the intact brain, multi-voxel pattern analysis was used in a series of event-related fMRI studies in a total of 46 healthy subjects. We predicted that activity patterns in this region would be determined by the identity of rather than the conceptual similarity between concrete entities. In a prior behavioral experiment features were generated for each entity by more than 1000 subjects. Based on a hierarchical clustering analysis the entities were organised into 3 semantic clusters (musical instruments, vehicles, tools). Entities were presented as words or pictures. With foveal presentation of pictures, cosine similarity between fMRI response patterns in right fusiform cortex appeared to reflect both the identity of and the semantic similarity between the entities. No such effects were found for words in this region. The effect of object identity was invariant for location, scaling, orientation axis and color (grayscale versus color). It also persisted for different exemplars referring to a same concrete entity. The apparent semantic similarity effect however was not invariant. This study provides further support for a neurobiological distinction between structural description knowledge and processing of semantic relationships and confirms the role of right mid-posterior fusiform cortex in the former process, in accordance with previous lesion evidence.
authors.affiliation: Laboratory for Cognitive Neurology, Department of Neurosciences, KU Leuven, Belgium; Neurology Department, University Hospitals Leuven, Leuven, Belgium.
authors.forename: Rose
authors.initials: R
authors.lastname: Bruffaerts
authors.forename: Patrick
authors.initials: P
authors.lastname: Dupont
authors.forename: Sophie
authors.initials: S
authors.lastname: De Grauwe
authors.forename: Ronald
authors.initials: R
authors.lastname: Peeters
authors.forename: Simon
authors.initials: S
authors.lastname: De Deyne
authors.forename: Gerrit
authors.initials: G
authors.lastname: Storms
authors.forename: Rik
authors.initials: R
authors.lastname: Vandenberghe
mesh_terms: D000293:Adolescent; D000328:Adult; D001931:Brain Mapping; D003210:Concept Formation / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D009778:Occipital Lobe / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D021641:Recognition, Psychology / Q000502:physiology*; D012660:Semantics; D013702:Temporal Lobe / Q000502:physiology*; D055815:Young Adult
keywords: Invariant object identity coding; Multi-voxel pattern analysis; Right fusiform gyrus; Semantics; Structural descriptions